Hot Stuff: NASA's Project FIRE
Updated: Apr 1
It's one thing to get to the moon, but another to return to Earth safely. Project FIRE (Flight Investigation of the Reentry Environment) was a collection of tests that obtained data about the aerodynamic and thermal conditions of returning to Earth from the moon. The two suborbital flights were crucial in the designing and composition of the Apollo heat shield.
Artist's rendering of a manned Apollo capsule during reentry (NASA)
In September 1960, the Langley Research Center proposed launching four reentry vehicles constructed from Mercury spacecraft on the Atlas-Agena B launch vehicle to "test conditions for high-speed reentry into Earth's atmosphere from the moon or beyond" (LePage, 2020). After the announcement of the Apollo program in 1961, Langley developed a new proposal called Project FIARE, or Flight Investigation of Apollo Reentry Environment, which swapped the modified Mercury spacecraft for sub-scale models of the new Apollo capsule and the Atlas-Agena B for the Atlas-Antares II [1].
NASA's Office of Advanced Research Technology announced Project FIRE on February 18, 1962 under the management of NASA Langley to support manned and unmanned reentry on lunar missions. The project aimed to develop a spacecraft capable of enduring reentry from a lunar flight (speeds of 24,500 miles per hour) through obtaining data on heat-shielding materials and heating rates. It also sought to verify the hypersonic flight and thermal characteristics of the Apollo spacecraft. a
Project FIRE engineer inspects sub-scale Apollo capsule (NASA)
According to a NASA Facts publication from 1965, Project FIRE faced three key problems: c
"Find a way to reproduce the typical reentry environment of spacecraft returning from the moon." The reentry speed of the capsule was predicted to be about 37,000 feet per second (7 miles per second, or 11.27 kilometers per second) with the angle of approach 15 degrees below the horizontal.
"Design sensors and measurement systems for the spacecraft and protect them from the severe reentry environment."
"Find a way to get the measured data away from the spacecraft and back to the Earth stations along the test range." The black-out during reentry would prevent real-time direct radio transmission and simply storing the data within the spacecraft was not an option since recovery of the vehicle after splashdown in the Atlantic Ocean was not financially feasible.
Ground-based tests were performed using the High Temperature Tunnel, the Thermal Structures Tunnel, and the Unitary Plan Wind Tunnel, each located at Langley in Virginia.
Technicians prepare a Project FIRE model for wind tunnel testing (NASA)
The launch vehicle of Project FIRE was the Atlas-Antares II, which put the payload on a suborbital, high ballistic trajectory to carry out its tests. The Atlas-D booster launched the manned orbital Mercury missions in 1962 and 1963. The payload consisted of a velocity package and a reentry package, both of which were contained within a clamshell-shaped fairing during ascent. The velocity package was the Antares A5 solid rocket motor, also called the Antares II, paired with a guidance, navigation, and control unit for stabilizing the reentry package and thrusting it back into the atmosphere.
The reentry package was a one-sixth model of the Apollo capsule with a base diameter of 26 inches (66 cm), a height of 21 inches (53 cm), and a weight of 220 pounds (99.8 kg). It contained multiple experimental scientific instruments, batteries, and telemetry transmitters, including three beryllium calorimeters that would be jettisoned in sequence during the three key phases of reentry and descent. b Also called the "flying thermometer", the little spacecraft and its analogues were built by the Republic Aviation Corporation [2].
Diagram of the Project FIRE payload (NASA)
Five minutes after liftoff at an altitude of 189.5 miles (305 km) and around 491 miles (790 km) downrange, the Atlas's engine would shut down and separate from the spacecraft. At T+15 minutes, the velocity package would reach an apogee of about 497 miles (800 km) around 2,423 miles (3,900 km) downrange. After coasting for a total of 21 minutes, the velocity package would ignite to spin the payload to 180 revolutions per minute. Six minutes later, the Antares would fire for thirty seconds to accelerate the capsule into the atmosphere before separating from the reentry package. Traveling just over 7 miles per second (11.3 km per second), the reentry package would also transmit data to a tracking station on Ascension Island, located in the Atlantic between South America and Africa. At around T+32 minutes and 5,126.3 miles (8,250 km) downrange, the reentry package would splash down into the ocean. No recovery of the spacecraft were planned and they are both still on the ocean floor.
Diagram of Project FIRE's mission profile (NASA)
FIRE I, mission #8 of the Apollo program, launched on April 14, 1964 from Launch Complex 12 at Cape Kennedy [3]. Reentering Earth's atmosphere at an angle of 14.5 degrees, the reentry package's speed was just over 25,166 miles per hour (40,501 km per hour), or almost 7 miles per second (11.27 km per second). The spacecraft's exterior reached a temperature of more than 20,000°F (11,400 K or 11,127°C). Due to a periodic fade-out of the transmitter, there was a partial loss of data at the receiving station at Ascension Island. According to a NASA Facts publication on FIRE I, about 60% of useful data was obtained. c FIRE I also held the record of fastest reentry speeds of an artificial object (to date).
FIRE II, mission #15 of the Apollo program, launched on May 22, 1965 and reached an apogee of over 500 miles (805 km). The reentry package reached a top speed of 25,400 miles per hour (40,877 km per hour) and a top temperature of 19,711°F (11,206 K or 10,933°C) during its descent to Earth.
FIRE II during launch on May 22, 1965 (NASA)
Project FIRE, though not well-remembered, was highly successful. The flights met all objectives and provided invaluable data on reentry heating, as well as new information on communications blackout. It also revealed the reentry heat load experienced while returning from the moon was lower than predicted, although this did not change the design of the heat shield. The first high-speed reentry of a flight-worthy Apollo spacecraft was in November 1967 during the unmanned Apollo 4 mission, the first flight of the Saturn V.
Author's note: This post was written entirely without the use of AI technology (sorry HAL). Thanks for reading and be sure to like and share this post!
[1] Its alternate name was Project Calorie
[2] North American Aviation built the full-size flight-worthy Apollo capsules
[3] Cape Canaveral was called Cape Kennedy from late 1963 (following President Kennedy's assassination) to 1973
Bibliography
"Fire I: The Reentry Heating Spacecraft." National Aeronautics & Space Administration. 1965, http://epizodsspace.airbase.ru/bibl/inostr-yazyki/nasa-facts/1965/Fire_I_The_Reentry.pdf c
Krebs, Gunter D. "FIRE 1, 2." Gunter's Space Page. https://space.skyrocket.de/doc_sdat/fire.htm a
LePage, Andrew. "Project FIRE: Testing Apollo's Reentry." Drew Ex Machina. 22 May 2020, https://www.drewexmachina.com/2020/05/22/project-fire-testing-apollos-reentry/ b
Reichl, Eugene. "Project Apollo: The Early Years, 1960 - 1967." Schiffer Publishing Ltd. 2016
"Hot Stuff" performed by Donna Summers; written by Pete Bellotte, Harold Faltermeyer, and Keith Forsey; produced by Pete Bellotte; released 1979